The invention relates to a jack for use in a radio or television receiver, taperecorder or the like and having internal contacts which are opened or closed upon insertion or withdrawal of a plug.
A conventional jack has a construction such that when a plug is inserted into the jack, a movable contact made of an electrically conductive, resilient material experiences an elastic deformation due to the plug inserted, thereby moving away from or into contact with a fixed contact. In such a conventional jack, since the movable contact is subjected to an elastic deformation each time the plug is inserted or withdrawn, a repeated insertion or withdrawal of the plug over a number of times results in a fatigue of the movable contact, causing a poor contact and limiting the useful life.
In order to overcome such a disadvantage of a conventional jack, it has been proposed to use a coiled spring which compensates for a reduction in the amount of elastic deformation experienced by the movable contact, thereby increasing the useful life. Such an improved jack is disclosed in U.S. Pat. No. 3,536,870 issued Oct. 27, 1970 and entitled "Jack with spring pressed resilient terminal". In the disclosed jack, a movable contact made from an electrically conductive, resilient material bears against a fixed contact in a resilient manner, and is additionally urged against the fixed contact resiliently by means of a coiled spring in order to increase the pressure of contact. Because a coiled spring is substantially less susceptible to fatigue than the movable contact, the disclosed jack obtaining an increased life as compared with one not incorporating a coiled spring. However, it should be noted that the patent premises the use of the movable contact comprising a resilient material in the similar manner as in the prior art, and the coiled spring is used for the purpose of supplementing the resilience of the movable contact when it is subjected to an elastic deformation. Consequently, the elastic deformation to which the movable contact is subjected upon insertion and withdrawl of the plug, as well as the earlier fatigue of the movable contact which occurs prior to the occurrence of the resilient wear of the coiled spring remain unchanged in this prior art jack, and in effect the insertion or withdrawal of the plug has been limited to the order of 20,000 times at most. In addition, the movable contact is bent in a V-configuration, for example, and it is a relatively difficult operation to press the movable contact of resilient material into such a definite bending angle. This results in variations in the shape of the movable contact formed from product to product, accompanying varying pressure of contact with its associated fixed contact. Where the degree of bending the movable contact is limited, and the movable contact is bent to a further degree to provide a sufficient pressure of contact with its associated fixed contact when it is assembled into the jack, the resulting movable contact will be liable to wear. Furthermore, the movable contact formed of a resilient material and the coiled spring will both experience their natural oscillation in response to an external shock or vibration to result in an unstabilized contact therebetween and also in the occurrence of noises. As another aspect, the movable contact is generally formed with a terminal at its one end which is extended to the exterior of a casing, and consequently, as a whole, it obtains a relatively large dimension. This means that it has a relatively high heat capacity, which may cause a thermal deformation in the casing molded from synthetic resin material when soldering a lead wire to such terminal, thereby resulting in a misalignment in the position or angle of the contacts, and thus disadvantageously producing a defective product. Finally, since a relatively expensive conductive resilient material such as phosphor bronze must be used for the movable contact, in addition to the use of the coiled spring, the cost of the overall assembly increases.
Therefore, it is an object of the invention to provide a long life jack.
It is another object of the invention to provide a jack which has a long life while assuring a sufficient pressure of contact with the fixed contact.
It is a further object of the invention to provide a jack employing a movable contact of a uniform and accurate configuration which can readily be pressed, thus assuring a given pressure of contact and a mechanically stability.
It is an additional object of the invention to provide a jack in which the heat capacity of the terminal for the movable contact is reduced, thereby rendering the casing insusceptible to deformation by soldering and avoiding the susceptibility to a change in the mounting condition of the contact.
It is still another object of the invention to provide a long life jack which assures a sufficient pressure of contact while avoiding the use of an expensive conductive, resilient material for the movable contact, thus enabling the jack to be produced inexpensively.